/Engine/Source/Runtime/Core/Public/GenericPlatform/GenericPlatformTime.h
Does per platform initialization of timing information and returns the current time. This function is called before the execution of main as GStartTime is statically initialized by it. The function also internally sets SecondsPerCycle, which is safe to do as static initialization order enforces complex initialization after the initial 0 initialization of the value.
current time
static double InitTiming()